1. Field of the Invention
This invention relates to generally energy management through heat recovery, and more particularly to systems, computer readable media, program code, and methods for providing enhanced energy management of mega industrial sites through energy recovery systems.
2. Description of the Related Art
The economics of industrial production, the limitations of global energy supply, and the realities of environmental conservation are an enduring concern for all industries. The majority in the world scientific communities believe that, the world's environment has been negatively affected by the global warming phenomenon due to the release of greenhouse gases (greenhouse gas) into the atmosphere.
There are three major sources of greenhouse gas: carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O). The world's CO2 emissions into the air have been increasing drastically over the past century. The industrial revolution and exploitation of natural resources such as coal and oil have greatly contributed to CO2 emissions. From greenhouse gas perspective, energy efficiency optimization is not only a fast track approach to reduce energy cost, but also to reduce energy-based greenhouse gas/CO2 emissions.
For decades, energy efficiency optimization merely addressed the energy efficiency of standalone process equipment. Since late eighties and early nineties, however, the landscape has changed. It is not only energy efficiency for the standalone equipment/unit but also for subsystems, systems, industrial complexes and today/future one mega sites as well as industrial cities through the utilization of heat exchanger network systems.
Heat exchanger network synthesis is a multi-variable multi-dimensional optimization problem in which the total network driving distribution depends on each stream conditions and each hot stream minimum approach temperature for heat recovery. Such variables can contribute to determining the number of units, shells, and both the heating and cooling utilities requirements as well as its mix. Utilizing conventional pinch technology, this multi-variable optimization problem has been reduced to a single variable optimization problem—the optimization of the global minimum approach temperature (ΔT_min) for each hot process stream of the problem. While such methodology can theoretically be used at any scale, it is still only utilized by others on standalone plants via direct intra-process integration between a plant's hot and cold streams. It is applied at the process level and has proved to be very successful in reducing both energy consumption and energy-based greenhouse gas emissions. Newer systems developed by the assignee of the invention or inventions described herein have provided further optimization through systems designed to develop an optimal set of stream specific minimum approach temperatures (ΔT_min_i) and advanced matching techniques.
Since the emanation of the pinch technology and its evolution to pinch analysis technique for process synthesis, direct integration has only been intra-process. Direct inter-processes integration has been considered by industry to be impractical. Arguments against utilization of such integration include arguments that: the processes that would be integrated may have different start up and shut down times; the processes can work at partial loads; the processes can have seasonal changes in its conditions; capital costs of utility systems, heaters and heat exchangers network may not be reduced over that of indirect inter-processes integration due to changes in processes schedule and operation philosophy; the disturbance in one process can propagate to another one if they are integrated, making the process difficult to control; the distance-time/velocity lags affect the controllability of processes; the geographical distances among processes will result in a substantial energy cost in pumping or compression and will require capital costs associated with the piping, pumping and compression; safety might be impacted due to the travel of a fluid from one hazardous area to another; and the fear of leakage and so on, which are very common to plant engineers. Additionally, systematic methods to handle mega sites and industrial zones for inter-processes integration are lacking and conventional mathematical programming models are not capable of handling mega size problems, where many facilities are involved in an industrial zone oversight. Therefore, direct inter-processes integration, while potentially very beneficial to energy conservation and greenhouse gas emissions reduction, is still to date not practiced in the mega industrial sites design and retrofit.
As such, the inventors have recognized the need for systems, computer readable media, program code, and methods that provide for the selection of direct integration among multiple plants/processes located in adjacent geographical locations while still considering indirect inter-processes integration to thereby optimize the waste energy recovery and reduce greenhouse gas.
The current methods for inter-processes integration are indirect, using buffer systems. The buffer systems are either steam system (most of the time) or hot oil system. Both research and industry have access to the pinch modified and mathematical programming methods which adapt the indirect method using steam system. Regarding utilization of steam, early pinch technology work on total site heat integration helped to determine levels of generation of steam to indirectly integrate different processes. Some researchers, however, have argued against using steam under certain scenarios because the generation of steam has to be accomplished at a fixed temperature levels, which may result in missed opportunities for integration, steam produced in most chemical complexes is also used to generate power, and that driving equipment and heating the steam to exactly match with process heating needs is almost impossible, and as such, usually result in venting and/or huge air cooling utilization. Further, it is not optimal to put waste heat boilers in the process plant to recover waste heat from one end and ignore the path of this steam in the whole facility, block or industrial zone and its end point. Additionally, in many hydrocarbon processing facilities, medium and/or high pressure steam generation or utilization not recommended for utilization in heating cold process streams, because of the fear of leakage to the hydrocarbon side and corrosion, and hence, is typically considered a forbidden match. Accordingly, some researchers have argued against steam utilization as a buffer in favor of hot oil system utilization.
Regarding utilization of hot oil, both research and industry also has access to the pinch modified and mathematical programming methods which adopt the indirect method using hot oil system. The researchers that favor hot oil over steam, however, have failed to mention that, in addition to the large number of hot oil circuits normally required to achieve the desired energy saving targets, the low heat transfer coefficient of the hot oil fluids result in heat exchangers requiring excessively large surface areas, more units needing to be added, and a larger number of start-up heaters and/or air coolers required per circuit, among others.
As such, neither sets of researchers, those favoring steam nor those favoring hot oil, advocate analysis or utilization of both hot oil and steam systems to provide indirect inter-processes integration. Accordingly, recognized by the inventors is the lack of a methodology that systematically identifies when the hot oil system, the steam system, or both provide the preferred solution on either the thermodynamic or economic basis. Additionally, recognized by the inventors is that no current method adopts both direct and indirect inter-processes integration methods; no conventional method adopts the direct inter-processes integration method for mega size problems such as integrated refining, petrochemical and chemical industrial zones; and correspondingly, no conventional method adopts both direct and indirect methods using both hot oil and steam systems. Additionally, it is recognized by the inventors that no conventional method considers the wider direct integration outside the industrial part of the complex with the community/housing part.
In summary, while the industrial community appears to agree that the direct integration approach in inter-processes integration (e.g., between several plants) may be more efficient and may render more saving in energy consumption and energy-based greenhouse gas emissions, it is not practiced, and prior to the designed processes of embodiments of the invention or inventions described herein, no systematic method to synthesis systems which exhibit such capability for mega industrial complexes exist. As such, the industry has a long felt, unsatisfied need for systems, computer readable media, program code, and methods to allow a user to synthesize energy recovery systems through utilization of direct and/or indirect inter-processes integration utilizing steam and/or hot oil systems, depending upon whether a decision-maker's focus is on thermodynamic or economic efficiency, or a balance between the choices.